U.S. Pat. No. 7,343,813, the entire content of which is incorporated herein by reference, describes a capacitive sensor array comprising a first and second plurality of parallel conductors separated by a compressible insulator. The second plurality of conductors are paired to partially overlap the first plurality of conductors, in two-by-one sets, whereby a force applied in a plane parallel to the conductor array will cause capacitance between the first and second conductors to change. In this context, “force” and “shear force” are interchangeable, and are defined as force(s) parallel to the X and Y planes. “Torque” and “moment(s)” are also interchangeable.
In accordance with the '813 patent, serially sampling the two-by-one conductor sets for changes in capacitance provide information on both the magnitude and direction of the force. In addition, forces applied perpendicular to the planes causes the insulator to compress, thus also changing the capacitances of the two-by-one sets of the sensor array. The imbalance of voltages between the paired conductors is applied to amplifier to sense force magnitude and direction. An embedded computer implements different functions to calculate the forces and moments. Compression force appears as an increase in peak voltage magnitude in both of the paired conductors.
While the configuration just described enables the detection of lateral force in X, Y and compression along the Z axis, the layout does not facilitate the sensing of all six components of the various forces and moments.